This invention relates to a circuit which provides voltage regulation to a utilization circuit while the normal supply of power thereto is available and which also limits the dissipation of a battery in a battery back-up circuit when the normal supply of power is disrupted, and the utilization circuit is thereafter operated from the battery.
Certain computer systems, for example, utilize dynamic random access memories (RAMs) which must be periodically refreshed in order to retain the data stored therein. Usually, these systems provide a battery, back-up circuit to refresh the RAMs in the event of a power failure. Generally, these back-up circuits are designed to provide power to refresh the RAMs for a time period of about 72 hours, which period covers a usual weekend in which a power failure may occur while the system may be left unattended. In some countries, it is necessary to disconnect the computer systems from the usual power receptacles as a safety measure when the systems are left unattended over a weekend, and in these situations, the battery back-up circuits are periodically used.
The batteries which are typically used in these battery back-up circuits are of the re-chargeable type. These batteries can be recharged after normal use providing that they are not drained beyond what is termed a "deep discharge" level. If they are drained beyond the deep discharge level, it is difficult to conveniently recharge them, and consequently, it may be necessary to replace them at considerable expense.